Bootloader
Overview
The Gamebuino uses the modified version of the Arduino's UNO bootloader (Optiboot). The changes allow the firmware to load and run the game selection sketch from SD card when the Gamebuild is reset with the C button held down; it also allows that software to load and launch other games on the SD card programatically. Other than these extra features the bootloader should run normally, meaning it is compatible with the Official software and will support IDE uploads and program verification.
Sources
- [1]: The firmware used by the official Arduino IDE for flashing Uno boards.
- 2boots, an SD-enabled bootloader source code, the Gamebuino bootloader uses it's FAT16 and flashing code.
Launching Loader
If the the C button is held down while the unit is powered-up then the bootloader will search for a compiled sketch on the SD card called "LOADER.HEX". Note that the SD must be formatted with FAT16 and the filename must be upper case characters.If no SD card is present, or if the LOADER.HEX file can't be found or loaded then the bootloader will execute whatever program is already flashed into memory.
Flashing the Gamebuino Bootloader
Under normal operation the Gamebuino is programmed via the USB virtual COM port with the device selected as "Arduino UNO". However, if you wish to program it or upload the bootloader using an external hardware programmer (e.g. another Arduino) then you must edit the boards.txt file in the Arduino package (typically loacted at C:\arduino-1.0.5\hardware\arduino\boards.txt) and add the following section:
gamebuino.name=Gamebuino gamebuino.upload.protocol=arduino gamebuino.upload.maximum_size=32256 gamebuino.upload.speed=115200 gamebuino.bootloader.low_fuses=0xff gamebuino.bootloader.high_fuses=0xd8 gamebuino.bootloader.extended_fuses=0x05 gamebuino.bootloader.path=gamebuino_boot gamebuino.bootloader.file=gamebuino_boot.hex gamebuino.bootloader.unlock_bits=0x3F gamebuino.bootloader.lock_bits=0x0F gamebuino.build.mcu=atmega328p gamebuino.build.f_cpu=16000000L gamebuino.build.core=arduino gamebuino.build.variant=standard
Restart the Arduino IDE and you will see a new device type called "Gamebuino". (This change is required for external programming because the Gamebuino bootloader is larger than the original Optiboot bootloader and the fuse bits need to be modified to accommodate this).
Launching Games via Software
The boot loader can be invoked at any time to load and launch a game from the SD card. To do this simply add the following code to any sketch:
#define load_game (*((void(*)(char*))0x7ffc))
A game can then be loaded and launched by calling this function, passing in an upper-case-only file name with the .HEX extension:
load_game("BLINK");
This causes a long-jump into the boot loader code causing it to load and launch BLINK.HEX from the SD card.
Questions, suggestions, solutions ?
If you have any questions, ask them the in this thread.
Good luck !